Systematic parameter screening for capillary electrophoresis monitoring of surfactants on silicon wafer surfaces by designed experiments

The surface purity of silicon wafers is an important parameter to monitor for yield improvement of semiconductor devices in a production line. Surfactants are used to reduce the surface potential in order to facilitate the removal or cleaning of particles and metals. Traces of surfactant residues from the cleaning bath may still be present on the wafer surface after the final cleaning step. In this report, two capillary electrophoresis (CE) methods for the analysis of dodecylbenzene sulfonate (DBS) are developed for monitoring the surfactant residues in the wafer manufacturing process. One method is developed for the sensitive determination of all DBS homologues and isomers in one single peak. Another method is developed for the fingerprint analysis of the homologues and isomers of DBS. The Taguchi methodology was used as a systematic optimization tool for the DBS analysis by CE. The experiments were evaluated by calculating the signal-to-noise ratio values with four responses. The lowest detection limit for DBS was 15 microg/L at 95% confidence level. The percent recovery of surfactant was between 90% and 110%.